Electrolytic manufacture of potassium persulphate



ELECTROLYTIC MANUFACTURE 0F1 POTASSIUM PERSULPHATE Filed March 5l, 1938 MonEsTo SALLERA-S` ATTYS.'

Patented Apr. 28, 1942 i ELECTBOLYTIC MANUFACTURE 0F POTASSIUM PEBSULPHATE Modesto Salleraararis, France, assigner to Buffalo Electro-Chemieal Company, Inc., a corporation of New York Appiiontio'n Maron s1, 193s, serisiNo. 199,294

`In France March 31, 1937 6Claims.

The direct manufacture of potassium persulphate by electrolysis of `an electrolyte containing only potassium salts has not been practised heretofore on account of the low efciency of the process. This low eiilciency is due `in part to the low ionic concentration of theelectrolyte used, in part to deposition Vof persulphate on the anode and in part to reduction which occurs at the anode.

'This invention relates to a process and to an electrolytic cell without` a diaphragm by means of whichpotassium persulphate may be obtained directly from potassium sans with` an energy eiliciency greater than that of the known processes. e Y

The essential feature of the process is Ithe' use of anelectrolyte in which` the potassium Ipersulphate formed by the electrolysis is nearly., insoluble (2.3 grams per litre of electrolyte at 15 C.).l This low solubility diminishes the reduction at the cathode of the Potassium persulphate formed electrolytically andV avoids the necessity of using a diaphragm.

Thisimproved electrolyte has a strong concentration of KS04 ion and H804 ion and a correspondingly good conductivity. Thegenergy consumption may be only 1.3 kilowatt-hours per kilo of potassium persulphate, the anodic current density being `0.5 amp. per square cin.4 'I'he use of this electrolyte results therefore in "a very good current and energy efilciency.

Examples of the y electrolyte of the present invention in which the potassium `persulphate is substantially insoluble are 3 moles-of potassium bisulphate (KI-1804) and one mole of sulphuric acid (H2804) with sufilcient water to give the following' composition:`

9s grams Hssotper litre 43o t Kasot '170 water i or 3'moles of potassium sulphate (KzSOD and 5` The electrolyte may also be `prepared from 1 other combinations of salts ofthe potassium and sulphate radicals, for example. by preparing a saturated aqueoussolution of potassium tetra- Asulphate KzSiOnBHzO and potassium bisulphate KHSO4 in the proportion of one mole of the former and two moles of the latter.

The` above examples relate to a temperature of 15 C. but the composition of the electrolyte is varied slightly with variation of temperature, but so that the potassium persuiphate is sub. stantially insoluble in the electrolyte.'

(Cl. 21M-82) The` electrolytic cell` comprises a substantially horizontal cathode of graphite in the form of a rectangular frame made upv of two long side plates and two short end plates or distance pieces.

The anode is formed by a row of vertical wires generally of platinum or indium-platinum, placed in the middle longitudinall line of the cathode frame. `The Wires are soldered or weldedto an iron frame covered by ebonite and fixedto the cathode to form a block which is supported as a.

whole in the cell whichmay be of sandstone.

This arrangement allows of a very short interelectrode space, a good current distribution and a very low electrical resistance. With the` aforesaid electrolyte and anodic current density the potential drop at the terminals is only about 3.a p volts.

To avoid deposition of persulphate at the anode "(which might diminish the `current and energy efficiency) compressed air is admitted into theelectrolyte below the electrodes and this together with the speed of upward now of the electrolyte has the desired effect. Besides, the

expansion of the compressed air will bringabout a substantial cooling of the electrolyte.

According to the invention, aconstant supplyl of e1eotro1yte is maintained at the iower part of the-cell and a constant discharge is provided at its upper part. 'I'he speed of upward flow of the `electrolyte and the compressed air forced into the electrolyte avoid the deposition of potassium persulphateat the bottom of the cell. y

The accompanying drawingillustrates the invention, and the preferred form of the cell:

Fig. 1 is a diagram of the cyclic process; n uFig. 2 is a vertical cross section through the ce Fig. 3 is a horizontal longitudinal section 'on 'line III-III 0f Fig. 2.

Referring to Fig. l, from a tank I0, the electrolyte flows by pipe Il to the lower part of the electrolysis cell l2, from the upper part'of which it passes through pipe I3 to a refrigerator Il andthence through pipe I5 to a lllter I6. 'The liquid leaving the iilter Itlpasses through pipe i1 finto the saturator IB where it receives any,

necessary additions of potassium and sulphate radicals. Pump 20 draws the regenerated elec-` trolyte throughl pipe i9 and delivers it through pipe 2l to the tank III.

The potassium persulphate leaves cell i2 in suspension' in the electrolyte and the quantity in suspension is increased during the flow through the refrigerator and the whole is retained by the filter IB from which it is periodically removed` 'Ihe electrolyte is then forwarded back at-tlie beginning of the cyclic process where it recovers its primary composition.

Referring to Figs. 2 and 3, the cell I 2` is pref- 60 erably constructed of stoneware and 'is shaped internally to form a support 22 for the cathode composed of four thick plates 23, 24, 25,` 26 fastened together to form a rectangle commensurate in length and `Width with the internal length and width of the cell. The means of assembling the plates (for instance screws)Y should be incapable of attack by the electrolyte. The current is conducted to the cathode by a graphite rod 21.

The anode consists of wires 28, preferably of iridium-platinum, held vertically in a metal frame composed of longitudinalV members 29 and 30 and vertical members 3l, 32 encased in ebonite or other suitable insulation. The lead for the current supply to the anode is shown at 34.

The pipe Il shown in Fig. 1 is extended as pipe 35 through the length of the lower part of the cell and is closed at its free end, the exit for the liquor being through perforations 36 along the topmost part of the pipe; thus the electrolyte'is fed uniformly throughout the length-of the cell. A outflow pipe I3 is at about`the level of the upper member 29 of the anodic frame.

sium persulphate electrolytically without the use of a porous diaphragm which comprises electro. lyzing aA substantially saturated aqueous solution of potassium bisulphate and sulphurie acid in substantially the mole relation of three moles of potassium bisulphate to one mole of sulphuric acid while maintaining such'a temperature and continuing the electrolysis that'a precipitate of 5 2. The continuous'method of producing potas-` sium persulphate electrolytically without the use of a porous diaphragm which'comprises electro- Vlyzing a substantially saturated aqueous solution of potassiumbisulphate and sulphurlc acid in substantially the mole relation of three moles of potassium bisulphate to one mole of sulphuric acid while maintaining such a temperature and continuing the electrolysis that a precipitate of potassiumpersulphate is produced, the solution subjected to electrolysis being continuously moved upwardly between the electrolyzing electrodes andV continuously removed from the cell at such a rate as to `carry out the precipitated potassium persulphate and prevent vdeposition of the same B5 in the cell or on the anode.

3. e rl'he continuous method of producing potassium persulphate electrolytlcally without the-,use

. of a porous diaphragm which comprises electro- `lyzing a substantially saturated aqueous solution of potassium bisulphate and sulphuric acid in substantially the mole relation of three molesof potassium bisulphate to one mole of sulphuric acid while maintaining such a temperature and continuing the electrolysis that a precipitate of potassium persulphate is produced, the solution subjected to electrolysis being continuously moved upwardly lbetween the electrolyzing electrodes and continuously removed fromI the cell at such a rate as to carry out the precipitated potassium persulphate and prevent deposition of the same in the cell or on the anode, compressed air being discharged into the solution passing between the electrodes to aid additionally in preventing deposition of solid potassium persulphate on the anode.

4. The continuous method of producing potassium persulphate electrolytically Without the use of a porous diaphragm which comprises electrolyzing a substantially saturated aqueous solution of potassium acid sulphate acidied with: sulphuric acid whilemaintaining such a temperature and continuing the electrolysis that a precipitate of potassium persulphate is produced, the solu- Vtion subjected to electrolysis being continuously moved upwardly between the electrolyzing electrodes`and continuously removed from the cell at such a Vrate as to Acarry out the precipitated potassium persulphate and prevent deposition of the same in the cell or on the anode, compressed air being discharged into the solution passing between the electrodes to aid additionally in preventing deposition of solid potassium persulphate on the anode.

5. The continuousmethodof producingpotassium persulphate electrolytically Without the'use of a porous diaphragmwhich comprises electrolyzing a substantially saturated aqueous solution of three .moles of potassium bisulphate and ilve moles of sulphuric acid whileg maintaining such a temperature and continuing the electrolysis that a precipitate of potassium persulphate is produced, the solution subjected to electrolysis being continuously moved upwardly between the electrolyzing electrodes and continuously removed from the cell at such a rate as to carry out the precipitated potassium persulphate and prevent deposition of the same in the cell or on the anode, compressed air being discharged into the solu-v tion passing between the electrodes to aid addi- 0 tionally inpreventing deposition of solid potassium persulphateon the anode.

6. The continuous method of producing potaslsium persulphate electrolytically without the use orav porous diaphragm which comprises electrolyzing 'a substantially saturated aqueous solution of two moles of potassium bisulphate and one mole of potassium tetrasulphate while maintain-i ing such a temperature and continuing the electrolysis that a precipitate of potassium persulphate is produced," the solution subjected to electrolysis being continuously moved upwardly betweentheelectrolyzing'electrodes and continuously removed from the cell at such arate as to carry outrthe precipitated potassium persulphate and prevent deposition of the same in the,

cell oron the anode, compressed air being tlis-A charged into the solution passing between they electrodes to aid additionally in preventing deposition o1 solid potassium persulphate on the anode. n

MODESTO SrpLERAS. 

